Electronic column gage

ABSTRACT

A sizing gage for use with an LVDT probe for producing an output signal representing the deviation of part dimension from a nominally ideal dimension, and a columnar display means comprising vertically arranged light emitting diodes for indicating the degree and sense; i.e., oversize or undersize, of part size deviation according to which of the emitting diodes is lighted. The probe output is an ac signal of polarity representing the degree of deviation. The probe output signal is converted to a dc voltage the amplitude and polarity of which is representative of part size deviation. The dc signal is used as a comparison base against a precision triangle wave signal to generate a squarewave the transitions of which occur at points in time related to the amplitude and polarity of the dc signal. This squarewave is compared to a reference squarewave of fixed transition time to produce a window pulse the width of which is representative of the degree of part size deviation. The window pulse gates clock pulses from a precision oscillator to a pair of decade counters to address a diode excitation matrix. The tens signal is gated to either the oversize light bank or the undersize light bank according to whether the time variable signal leads or lags the fixed time signal. Nulling and range setting circuit details are disclosed.

This invention relates to gaging devices for indicating the sizedeviation of a machined part or the like from a predetermined nominallyideal size.

BACKGROUND OF THE INVENTION

In the course of machining precision parts it is customary to check thepart for size by comparing it to a part of nominally ideal or perfectsize. One prior art apparatus for accomplishing this comprises avertical glass tube through which air is caused to flow in varying ratesaccording to the size deviation of a part under inspection. The verticalair column supports an indicator float in a vertical position which isrelated to part size. Thus, a given float position may be equated toideal or mean size while positions above and below the given positionmay be equated to part sizes which are over and under the mean value,respectively.

The columnar display format of the pneumatic size gage is highly favoredin view of the graphic character thereof and the ease with which partsize may be compared to tolerance limits. However, the pneumaticcharacter of the gaging device described above is disadvantageous fromthe standpoint of cost, maintenance, and adaptability to expanded datagathering, processing, and display functions. Accordingly, it isdesirable to provide an entirely electronic implementation for a gagepreferably utilizing the columnar display format and having thecharacteristics of high accuracy, simplicity of operation, low cost andadaptability to additional display and/or data gathering and processingfunctions.

BRIEF SUMMARY OF THE INVENTION

The principal object of the present invention is to provide anelectronic apparatus for measuring and indicating the size deviation ofa machined part or the like from a nominally ideal size and being ofsuch character as to be compatible with a columnar type display unit. Ingeneral, this is accomplished by a gaging system adapted to work incombination with a probe or transducer device, such as a linear variabledifferential transformer probe (LVDT), which generates an electricalsignal quantity the analog character of which is related to part sizedeviation. This system further comprises means for converting the analogsignal to a digital signal representing the absolute value of part sizedeviation, a second signal for indicating the sense, either positive ornegative, of size deviation, and display means responsive to thecoincident application of these two signal quantities to excite aselected visual display element such as a light emitting diode (LED) ina columnar display.

A second feature of the invention is the novel means by which aconventional analog-type LVDT probe signal may be converted to digitalform so as to be readily applied to a digital signal responsive controlmeans for selecting one out of several separately actuable displaydevices. In addition, the digital signal may be applied to moreextensive data processing apparatus such as a microprocessor. In generalthis is accomplished by generating a repeating waveform such as asquarewave, which varies in timing in accordance with measured partsize, generating a pulse count representing the time difference betweenthe repeating waveform and a reference, and utilizing the pulse count asat least a part of an address to be input to a control circuit for alight-emitting diode display. In the preferred form, a sign signal isalso generated by determining the relative leading or laggingrelationship between the repeating waveform and a reference waveform.The sign signal is thereafter used as a second component of the addressto be input into an LED display matrix which operates in a coincidentsignal address selective mode.

Still another feature of the invention is the accuracy and stability ofa true ac zero as opposed to a dc bias or offset zero, together withmeans for accurately and positively establishing the zero or ideal partsize condition. In general, this results from the combination of aprobe, such as an LVDT, generating an ac signal which varies inamplitude, either positively or negatively, according to the part sizedeviation, means for producing a variable amplitude dc signal whichrepresents the peak value of the ac signal amplitude, and analog todigital converter means as described above for effectively convertingthe variable amplitude dc signal into a time shifting wavefront whichmay be compared to a fixed time wavefront to generate a "window" which,in turn, is used to gate pulses from a stable clock source into acounter. This combination further comprises a zeroing apparatus which isassociated with the probe in such a way as to mix a selectively variableportion of the probe excitation signal with the probe output signal toestablish an ac signal, the null value of which represents the zerocondition, all actual measured part size deviations having the effect ofmodulating the ac signal either positively or negatively from thepre-established zero as described above.

Another feature of the invention is the generation of an accuratedigital count representing part size by gating pulses between crossingtimes of a variable dc signal and a triangle wave. This feature resultsfrom the use of a phaselocked loop connected to the triangle wave sourceto generate the count pulses, thereby automatically compensating for anyvariations which might occur in the triangle wave due to oscillatordrift, line voltage change and so forth.

Still another feature of the invention is the use of a novelcoincidental address technique whereby one of a large number ofindividually excitable display devices may be selected for excitationaccording to the measured part size using only two address bits, both ofwhich are derived by the electronic gaging circuitry from the analogsignal output of a conventional probe device. As hereinafter describedin greater detail this is accomplished through the use of light-emittingdiodes which, although physically arranged in column, are electronicallyarranged in a coincidently addressable matrix such that only twocoincident bits are necessary to select any one of the relatively largenumber of LED's in the matrix for excitation.

Many additional features and advantages of the invention including theadaptability of the subject device to limit detectors and to moresophisticated data processing and/or display functions will be apparentfrom a reading of the specification in which an illustrative embodimentof the invention is described in detail. This specification is to betaken with the accompanying drawings in which the various structural,electronic, and functional characteristics of the preferred embodimentare illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the electronic circuitry interconnecting anLVDT probe with a columnar display device having light-emitting diodedisplay elements;

FIG. 2 is a more detailed circuit diagram of the portion of the circuitof FIG. 1 including and immediately adjacent the signal generatingprobe, and illustrating the zeroing and scale setting apparatus;

FIG. 3 is a timing diagram useful in explaining the operating of thecircuit of FIGS. 1 and 2;

FIG. 4 is a detailed circuit diagram of a representative portion of thedisplay system and the circuitry for addressing the display system;

FIG. 5 is a detailed circuit diagram of a representative portion of anactual LED coincident current selection connection;

FIG. 6 is a timing diagram useful in explaining the operation of thecircuit of FIGS. 4 and 5;

FIG. 7 is a circuit diagram representing the option of aninterconnection of the subject device with a limit detector;

FIG. 8 is a perspective drawing of the outer housing, display panel andadjustment knobs of an actual device constructed in accordance with theinvention; and,

FIG. 9 is a cross-sectional drawing of the display scale strip of thedevice of FIG. 9 illustrating the fashion in which it is removablysecured to the housing.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT FIG. I

FIG. 1 of the drawings shows an LVDT probe 10 having a plunger typecontact 11 for measuring the vertical dimension of a face ground part 12which is resting upon a precision base 14. Probe 10 produces an outputsignal which is applied to a column gage 16 to excite one of a pluralityof vertically linearly arranged LED indicators 18. The indicators 18 ofcolumn gage 16 include a centrally located indicator 18a which, whenexcited, indicates that the part 12 corresponds in vertical dimension toa predetermined nominally mean dimension; i.e., there is no detectabledifference between the measured dimension and a preestablished ideal ormean value. Indicators 18 arranged vertically above central indicator18a represent increments of variation above the mean size whereasindicators 18 vertically below central indicator 18a representincrements of variation below the mean size. The indicator 18a ispreferably green and the remaining indicators are red, although anyother color or combination of colors may be employed as desired. Columngage 16 may bear a permanent or replaceable legend strip 19 indicatingthe value of the increments. The tolerance values for a given part maybe set by clear plastic snap-on slide overlay elements 21a and 21b. Itwill be understood that in the typical column gage, many more indicatorsare found than are indicated in the drawing of FIG. 1; e.g., onecommercially available embodiment bears fifty-one LED's.

The circuitry of FIG. 1 is employed to select for excitation oneparticular indicator 18 in accordance with the character of a signalwhich is generated by the LVDT probe 10 as hereinafter described.

A time base for all portions of the system of FIG. 1 is provided by amaster oscillator 20 which produces a 20 Hz squarewave output forapplication to a phase-locked loop 22. The output of the phase-lockedloop 22 is a stable 163.8 KHz periodic waveform which is applied to amultiple tap frequency divider 24, from which a 20 Hz signal isconnected back to the phase-locked loop to provide phase stability aswill be apparent to those skilled in the art. A 5,120 Hz signal fromanother tap of frequency divider 24 is applied through a squarewaveamplifier 26, band pass filter 28 and ac amplifier 30 to the LVDT probe10 as an excitation signal. The filter 28 filters squarewave harmonicsand results in the application of a sinusoidal waveform to the probe 10.

Probe 10, which is described in more detail with reference to FIG. 2,produces an output signal of alternating voltage which varies inamplitude approximately ± 10 volts peak-to-peak depending upon thevertical dimension of part 12 measured by probe 10. As hereinafterdescribed, the output of amplifier 32 connected to probe 10 is adjustedvia dial 120, also shown on display 16, such that a part of mean sizeproduces an output signal of zero amplitude whereas an off-size partproduces a signal of an amplitude representative of the deviation. Theoutput signal from probe 10 is applied through amplifier 32 and adecoupler comprising capacitor 34 and resistor 36, to a sample gate 38which is triggered by a 5,120 Hz signal from frequency divider 24 tosample the ac probe signal precisely at peak. This is accomplished byconnecting the 5,120 Hz and 10,240 Hz output of divider 24 to amonostable multivibrator or "one shot" 40 which triggers the sample gate38 at a time which is phase-locked to the excitation of the probe itselfas is apparent from inspection of the circuitry of FIG. 1. The pulseoutput duration of the one shot 40 determines the sample pulse width.Decoupler 34, 36 filters out any dc component which might appear in theoutput of amplifier 32 and eliminates signal drift.

The amplitude signal which is passed by sample gate 38 is applied as arepeating pulse to a large capacitor 42 such that the stored voltage oncapacitor 42 is, after a few sample cycles, a dc voltage the amplitudeof which is representative of the measured part dimension. The voltageon capacitor 42 is positive relative to ground for size deviations ofone sense and negative for deviations of opposite sense. The advantagesof this approach to converting the probe ac signal to a dc value includethe fast rise time (if desired) of the dc signal on capacitor 42, thus,giving fast response to signal level changes, and the elimination of anysignal leakage back through gate 38 to previous circuit components.

To determine whether the part is oversize or undersize, the measuredpart dimension signal, i.e., the dc voltage on capacitor 42, is appliedby way of conductor 44 to the negative input of one of two identicalop-amp comparators 48 and 50. The function of comparators 48 and 50, andcircuitry to be described, is to convert the dc voltage which is ananalog representation of measured part size deviation to a digitalsignal for digital data processing.

To accomplish the A/D conversion, a 20 Hz triangle waveform from masteroscillator 20 is applied via line 46 to the positive inputs of eachcomparator 48 and 50 to serve as a time reference. The negative input ofcomparator 48 is connected to ground. Comparator 48 produces asquarewave 52 having transitions which correspond to the crossing of thetriangle and the ground reference. Accordingly, the positive andnegative-going transitions of squarewave signal 52 are fixed in timerelation to the output of the master oscillator 20. When the signal oncapacitor 42 is zero, the transitions of waveform 54 from comparator 50are coincident in time to those of waveform 52. Variation in the dclevel of the signal on line 44 results in production of a squarewave 54the transitions of which either lead or lag those of wave 52 accordingto when the triangle wave equals the dc signal amplitude; waveform 54leads waveform 52 for oversize parts and lags for undersize parts, thedegree of lead or lag depending on the part size deviation.

The relative times of two squarewaves 52 and 54 are determined byapplying the outputs of comparators 48 and 50 to the inputs of anEXCLUSIVE OR gate 56, the function of which is to generate a windowpulse at the twenty Hz frequency but varying in width according to thetime difference or phase difference between the two square waveforms 52and 54. In other words, the output of gate 56 is high whenever the inputsignals thereto are different but is low whenever the two signals arethe same. The output of gate 56 is connected to one input of AND gate58. The other input of AND gate 58 is connected to receive a 163.84 KHzsignal from phase-locked loop 22 by way of conductor 60. This highfrequency signal is, in effect, a clock signal which is passed whenevera window pulse is applied to the AND gate by gate 56. Since the windowpulse varies in width, the number of pulses passed for each window issubject to variation depending upon measured part dimension; i.e., apart having a dimension which deviates from the mean produces repeatingclock pulse bursts having a given number of pulses, and that pulsenumber is a direct indication of the deviation from the ideal dimension.A part of ideal size produces no pulses.

The pulse burst, if any, is applied through AND gate 62, which isenabled by the twenty Hz signal from oscillator 20, to a frequencydivider 64. Divider 64, which is actually a decimal counter, produces anoverflow pulse for every ten input pulses. The AND gate 62 has theeffect of looking at only the pulse bursts during the positive half ofthe 20 Hz waveform, and divider 64 has the effect of ignoring pulsecount increases of less than ten thus to avoid exciting the indicator 18representing the next increment of size deviation until a full sizedeviation is in fact measured.

The overflow pulses from frequency divider 64 are applied to a firstdecade counter 66 which forms part of the circuitry for addressing theindicators 18 in the column gage 16 as hereinafter described. Overflowsfrom counter 66 are connected to a second decade counter 68. The countin counter 66 represents the "ones" digit in the pulse count whereascounter 68 represents the "tens" digit. The ten output lines fromcounter 66 are connected to provide first inputs to the addressablecontrol 70, the sign logic being effective to select either theundersize indicator bank or the oversize indicator bank in display 16,depending on the sense of the size deviation.

To determine the sign or sense of the deviation, the fixed and variablephase squarewave signals 52 and 54 from comparators 48 and 50 areapplied as opposite inputs to a D-type flip-flop 74 to set or reset theflip-flop according to the leading or lagging condition of waveform 54relative to waveform 52. The two outputs of sign flip-flop 74 areconnected to opposite inputs of sign control logic 72 to enable gateswhich control the excitation of either the upper or lower bank ofindicators 18 in column gage 16 depending upon whether the part measuresoversize or undersized. In other words, the number of pulses in theburst of pulses passed by AND gate 58 is an indication of the absolutesize deviation whereas the sign signal from flip-flop 74 is anindication of the sense or direction of size deviation, either oversizeor undersize. The details of the counters 66, 68, control 70, logic 72,and a reset 137 and blanking control unit 140 are described withreference to FIGS. 4 and 5.

FIG. 2

The probe 10 is shown in FIG. 2 to comprise an inductive coil 80 dividedinto upper and lower parts 82 and 84 by a center tap and connected toreceive the 5,120 Hz output of amplifier 30 as an excitation signal. Avoltage divider comprising resistors 86 and 88 is connected across coil80. The primary winding 90 of a small output transformer is connectedbetween the center tap of coil 80 and the junction between the voltagedivider resistors 86 and 88. A secondary winding 92 which is inductivelylinked to primary winding 90 has opposite ends thereof connected throughamplifiers 94 and 96 to the amplifier 32, the output of which isconnected through RC circuit 34, 36 to the sample gate 38 as previouslydescribed.

The voltage which appears across primary 90 is a function of theelectrical balance between coil portions 82 and 84 which, in turn, iscontrolled by the position of a ferrite tuning slug 98 which ismechanically connected to the part contact 11 as previously described.Variation in the vertical dimension of part 12 operates through contact11 to displace the slug 98 relative to the coil portions 82 and 84 tovary the impedance balance therebetween. When the currents through theupper and lower loops represented by coil portions 82 and 84 and voltagedivider resistors 86 and 88 are equal, the loop currents cancel throughprimary 90 and no output or secondary voltage is generated. As the loopcurrents become unequal a voltage is generated in the secondary winding92, the magnitude and phase of which is representative of the degree anddirection of slug displacement. For example, if the part 12 is slightlylarger, slug 98 is displaced upwardly increasing the impedance of coilportion 82 and decreasing the impedance of coil portion 84. This has theeffect of decreasing the current in the upper loop and increasing thecurrent in the lower loop causing a voltage to be impressed across coil90, the amplitude of which is representative of the extent ofdisplacement of slug 98 and the polarity or phase of which isrepresentative of the direction of displacement of slug 98. If, on theother hand, the part is smaller, slug 98 moves downwardly to decreasethe loop current in the lower section of the probe circuit causing avoltage of opposite phase or polarity to be generated in the secondarywinding 92.

When a part of ideal or mean dimension is placed in the probe 10, theposition of the contact 11 and the slug 98 is mechanically adjusted toproduce a substantially balanced condition. Thereafter, an electronicadjustment must be made within the circuitry of FIG. 2 to zero or nullthe display unit 16. To accomplish this a second voltage dividercomprising resistors 100 and 102 is connected across the coil 80 inparallel to voltage divider resistors 86, 88 and a variable wiper 104 isconnected between resistor 102 and the input of an operational amplifier106, the output of which is connected through resistor 108 to an inputof amplifier 94. Thus, by varying the position of the wiper 104 onresistor 102 a selectively variable portion of the 5,120 Hz excitationsignal can be algebraically mixed with the output signal appearingacross secondary 92 to establish an ac zero at the output of amplifier32; i.e., the position of wiper 104 is varied until the inputs to theamplifier 32 are exactly the same. At this point, the output ofamplifier 32 is zero and the sample voltage passed by gate 38 to thestorage capacitor 42 is zero.

The circuit of FIG. 2 also discloses means for adjusting the scale orrange of the device. This includes a resistor network 110 and a variableposition selector wiper 112 connected across the gain set inputs ofamplifier 32 such that moving the wiper 112 between the taps of theresistors in network 110 effectively varies the gain of amplifier 32 andthus the magnitude of the output signal which is generated for any givenincrement of displacement of tuning slug 98. The resistors in network110 are of such varying value as to produce suitable range variations inmeasurable part size deviation.

The circuit of FIG. 2 further comprises means for temporarily andinstantaneously increasing the gain of amplifier 32 during the zeroingoperation thereby to provide a "zero magnification" function whereby thedisplay unit may be fine-tuned to the null or zero condition using ahigh gain setting which is thereafter reduced for normal measurement.This ensures that the original zero setting is not off by some smallamount which, at the current gain setting, indicates less than a fullincrement of displacement in either the positive or negative direction.

To accomplish this a spring-biased push button 114 is connected inseries with a resistor 116 across the gain set terminals such thattemporary depression of the push button 14 results in a temporary highgain setting of amplifier 32. Push button 114 is preferably mechanicallycombined with the range switch 118 on the display unit 16, it beingunderstood that rotation of the switch 118 varies the angular positionof wiper 112 for range selection. In other words, switch knob 118 isrotatable for range selection purposes but may be depressed against theforce of a bias spring for temporary zero magnification during which oneadjusts knob 120. It is understood that the shaft to which know 120 isattached is interconnected with the wiper 104 to vary the positionthereof on the voltage divider resistor 102.

The LVDT probe comprising center tap coil 80, slug 98, and contact 11 isa commercial product which may be purchased from Brown & Sharpe; ModelGT-21 has been found to be satisfactory in actual use.

A summary of the operation of the circuit as described with reference toFIG. 2 will now be given with specific reference to the waveformdiagrams of FIG. 3.

FIG. 3

FIG. 3 shows two sets of waveforms which result in the circuits of FIGS.1 and 2 under certain part measurement conditions. In each case it isassumed that the output from amplifier 32 of probe 10 has been adjustedto null with a part of mean dimension.

The top left portion of FIG. 3 is an example of the waveforms generatedby placing an oversize part in the probe apparatus of FIG. 10. Underthese conditions, the tuning slug 98 is displaced away from the balancedor zero condition such that an ac voltage is generated across secondarywinding 92 of the probe output transformer; this voltage is representedby waveform A in FIG. 3. A sample pulse B is applied by one shot 40 tothe sample gate 38 on each cycle of the probe output voltage to apply apositive signal of an amplitude representing the degree of part sizedeviation to the storage capacitor 42 such that a positive voltagerepresented by waveform C is ultimately generated. This voltage iscompared to the triangle reference D in comparator 50, the output ofwhich is the waveform 54 shown in FIG. 3. It will be noted that thetransitions in the waveform 54 coincide with the intersections betweenthe triangle wave D and the capacitor voltage C; since the capacitorvoltage is positive the leading edge in waveform 54 occurs later in timethan the leading edge of square waveform 52 also shown in FIG. 3. Thewindow pulse E produced by EXCLUSIVE OR gate 56 is equal in duration tothe time difference between the leading edges of waveforms 52 and 54 andgates pulses through gates 58 and 62 to present pulse burst F to thecounters 66 and 68 are previously described. Note that pulses in burst Foccur after the leading edge of square waveform 52. All waveforms aresynchronized by the phase-locked loop 22 and divider 24 to establish theproper phase relationship and to compensate for signal drift due to linevoltage and temperature changes. In other words, a given number of countpulses always corresponds to a cycle of the triangle wave regardless ofvariations therein.

In the second example shown in FIG. 3 the probe voltage A' is negativeindicating an undersize part and a shift of the slug 98 in such adirection as to unbalance the probe output transformer as previouslydescribed. The voltage is again sampled by pulses B but results in anegative charge on capacitor as represented by waveform C'. Thiswaveform is again compared to the triangle D and the intersectionsrepresent transitions in waveform 54 as shown. However, since the dcsignal level C' is negative, the leading edge in waveform 54 precedesthe leading edge of waveform 52 and results in an early generation ofthe window pulse from gate 56. Accordingly, the pulse burst H generatedfor the undersize part precedes the leading edge of waveform 52.

By way of overall summary, it will be recalled that the number of pulsesin each of the bursts F and H is representative of the degree of partsize deviation and the time relationship between the leading edges ofwaveforms 52 and 54 is representative of whether the part size deviationis over or under the mean size.

FIGS. 4 and 5

FIGS. 4 and 5 are detailed circuit diagrams of representative portionsof the display control circuitry in the unit of FIG. 1.

In FIG. 4 the indicators 18a, 18b, and 18c are light emitting diodes andare connected into a matrix 70 representing the addressable controlcircuitry of FIG. 1 and comprising a grid of conductor rows and columns;the term "row" being arbitrarily assigned to the horizontally extendinglines in FIG. 4 and the term "column" being arbitrarily assigned to thevertically extending lines in FIG. 4. Each LED indicator 18 iselectrically connected between a row conductor and a column conductorsuch that coincident interconnection of the selected row and columnconductors to a voltage source and ground, respectively, is operative tobias the LED interconnected between those two selected conductors into alight emitting condition.

Decade counter 66 representing the units for ones value of the pulsecount is shown connected to receive the clock pulse burst and has anoverflow line 120 connected to the input of decade counter 68 torepresent the tens digit of the pulse count. The decimal output linesnumbered 0 through 9 of counter 66 are connected through a currentbuffer 122 to the row conductors of the addressable control matrix asshown. Since there are 51 LED indicators in the preferred display unit16, it is necessary to use only the first three outputs numbered 0through 2 of the tens counter 68. These outputs are connected throughsign logic gate bank 72 and a second current buffer 124 to the verticalcolumn lines of the LED excitation matrix 70. Logic gate bank 72comprises six identical AND gates 72a through 72f. Gates 72a and 72deach have one input connected to the zero output of decade counter 68,gates b and e each have one input connected to the one output of decadecounter 68 and gates c and f each have an input connected to the twooutput of counter 68. All of gates a, b and c have the second inputconnected to the lead pulse output line 126 from sign flip-flop 74 ofFIG. 1 such that all three gates 72a, b and c are enabled for theundersize part measurement condition; i.e., the leading edge of waveform54 precedes the leading edge of waveform 52 as previously described.Similarly, the lag pulse line 128 from sign flip-flop 74 of FIG. 1 isconnected to all three gates 72d, e and f to enable all three gates foran oversize part measurement. The result of the gates 72 is to enableone group of column lines for oversize parts and another group of columnlines for undersize parts. The first group of column lines is associatedwith the upper LED indicators on display 16 and the second group ofoutput column lines is associated with the lower LED indicator set ondisplay unit 16.

The operation of the circuit of FIG. 4 will be described by reference tothree specific examples. In all cases, a reset pulse on line 130initializes counters 66 and 68 to zero.

First assume a part which is undersize by twelve increments of measureis placed in probe 10. It is thus desirable to excite LED indicator 18bwhich is located on the scale of display 16 in the twelve incrementposition of the undersize portion of the scale. A pulse count of twelvecauses output row line 2 of decade counter 66 to go high producingone-half of the necessary selection signals for LED indicator 18b. Thetenth pulse received enables overflow line 120 to decade counter 68 andadvances the counter from the zero to the one condition causing an inputsignal to be applied to both gates 72b and 72e. If the part isundersize, line 126 is high while line 128 is low. Hence, only gate 72breceives both enabling inputs thus to excite the -10 column line whichcompletes the selection of LED indicator 18b.

As a second example assume that a pulse count of twelve is received butthat the part is oversize; hence, it is desirable to select forexcitation LED indicator 18c. The 2 output line of decade counter 66 isagain selected for excitation and the 1 output line of decade counter 68is again selected for excitation. However, for an oversize part onlyline 128 is high thus to complete the selection of gate 72e. Thisexcites the column line +10 needed to complete the selection forexcitation of LED indicator 18c. In each case, the two counters supplyrow and column selection bits and flip-flop 74 supplies a sign bit tosteer the column bit to the correct LED group, either plus or minus.

If a zero pulse count is received, the reset pulse on line 130 haspreviously reset both counter 66 and 68 to the zero condition selectingthe uppermost row conductor as well as one input to each of gates 72aand d. The sign flip-flop 74 will simply remain in whatever state itfinds itself thus causing either line 126 or 128 to go high. If line 126goes high, gate 72a is enabled to complete the selection to indicator18a through diode 132. If, on the other hand, line 128 is high, gate 72dis selected to energize indicator 18a through diode 134. Diodes 132 and134 are connected together in a common OR junction such that a zeropulse count of either polarity operates to excite indicator 18a.

FIG. 5 is a schematic circuit diagram of the buffer connections 122 and124 necessary to light a given LED indicator 18. Buffer 124 comprises aplurality of transistors such as 124a the collectors of which areconnected to a 12-volt source and the emitters of which are connected toone side of the diode indicators 18 as shown. Buffer 122 comprises asimilar bank of transistors such as 122a, the collector electrodes ofwhich are connected to the other terminals of the diode indicators 18and the emitters of which are connected through current limitingresistor 136 to ground. The counter outputs are connected as base drivesignals to the transistors in buffers 122 and 124 to control theconductivity thereof; such transistors, except those selected, beingnormally biased to the off condition. Thus, when the LED indicator 18 isselected by the counters 66 and 68, base drive signals are applied totransistors 122a and 124a to render the transistors conductive and tocomplete a series circuit from the 12-volt source through the collectorto emitter circuit of transistor 124a, through a portion of a columndrive line, the LED indicator 18, a portion of the row line conductor,the transistor 122a and the resistor 136 to ground. Current flow throughthe LED indicator causes it to emit light as is well known to thoseskilled in the art.

A blanking function is desirable to prevent a short term excitation ofLED indicators 18 between zero and the selected indicator during thecount up portion of each pulse burst. This can be accomplished byconnecting transistor 138 in parallel shunt relationship with each ofthe transistors 122a in buffer 122 to apply a 12-volt signal to theemitter electrode of all transistors in buffer 122 until the count-upsequence has been accomplished. A control signal to the base oftransistor 138 is provided by connecting the 20 Hz squarewave signalfrom master oscillator 20 through a dwell unit 135 which produces afixed delay, a reset pulse source 137 and second pulse 140 to the baseelectrode of transistor 138 to bias the transistor on. This places thesame potential on both sides of the diodes 18 to prevent the excitationof any LED indicator until the count-up sequence has been accomplished.The reset and delays may be accomplished by means of a simple one shotmultivibrator, as will be apparent to those skilled in the art.

FIG. 6

FIG. 6 is a waveform timing diagram which is representative of a typicaloperation of the circuitry of FIGS. 4 and 5. FIG. 6a shows the 20 Hztiming signal whereas FIG. 6b shows the triangular waveform. FIG. 6cshows a dwell pulse which is output from the one shot 135 in FIG. 1beginning with the leading edge of the 20 Hz signal. The reset pulsefrom unit 137 is illustrated on line d of FIG. 6 whereas the blankingpulse 6e is shown to be triggered by the trailing edge of the resetpulse as previously described. Both the plus and minus count pulsebursts occur within the blanking time thus to produce the actualcount-up function. Accordingly, only the finally selected LED indicatorwill actually be excited to produce a visual display.

FIG. 7

It is often desirable to employ, in combination with the basic displayfunction provided by the apparatus of FIGS. 1 and 2, an indication thatsome undersize limit is exceeded such that machine shut-down can beconsidered or automatically effected. For example, an indication may beproduced whenever a part is at least 21 increments of measurable partsize deviation below the mean value. The circuitry of FIG. 7,representing a very modest addition of components over those alreadypresent in the circuitry of FIGS. 1 and 2, may accomplish this purpose.

In FIG. 7 the output lines of the units counter 66 are connected to tapswhich are individually selectable by means of a manually positionablewiper 200 which sets the units value of the limit to be detected. Theoutput side of wiper 200 is connected to one input and an AND gate 202.The other input to AND gate 202 is taken from a manually positionablewiper 204 which may be positioned on the output tap of any one of thethree AND gates 72a, 72b and 72c representing the three tens digits ofthe undersize condition. For a limit of -21, wiper arm 200 is set to the-1 position while wiper 204 is set to the -20 position such that theoutput of gate 202 is high whenever a pulse count of -21 in thebelow-mean direction is produced. Similar circuitry utilizing wipersconnected to counter 66 and gates 72d through 72f provides a signal tothe other input of OR gate 206 to provide the oversize indication. Theoutput of gate 206 is connected to the set input of a flip-flop 208, theopposite input being connected to the reset line 130 as shown. The 1output of flip-flop 208 is connected to an indicator 210 such as a lampor buzzer to give a visual or audible indication that the present limithas been exceeded. Wiper arms 200 and 204 are, of course, connected tomanually manipulable devices such as thumb wheels or dials foradjustment to other limits. Visual indicator 210 may, of course, bereplaced with a direct feedback connection from flip-flop 208 to themachine which is making parts to effect an automatic shut-down ifdesired.

FIGS. 8 and 9

FIGS. 8 and 9 illustrate a preferred packaging of a display unit 16constructed so as to be easily operated as well as to be electricallyinterconnected with additional display units such as 16' in FIG. 8.

The unit 16 comprises the upright housing 211 which is rearwardly angledfor ease of reading and which is disposed atop a base portion 212comprising a power supply for the electronics illustrated in FIGS. 1 and2. A panel on the hidden side of housing 211 may be removed to provideaccess to at least some of the interconnect circuitry and to facilitatethe installation of additional units such as 16' in FIG. 8.

The LED indicators 18 are arranged in a vertical row with the greenindicator 18a disposed in the center. The zero adjust knob 120 and therange selector 118 are disposed beneath the scale 19 as previouslydescribed.

Scale 19 takes the form of a plastic strip which slides from the topinto a bracket 214 secured to a plate 215 on the front of the uprighthousing 211. The left and right sides of scale strip 19 have asilk-screened pattern of numbers disposed thereon and the center stripis left transparent to permit viewing of the LED indicators 18. One sideof strip 19 may be printed with one or more scales in one range groupwhile the other side may be printed with scales in another range group.Accordingly, it is possible to simply slide the scale strip 19 out ofthe bracket 214, reverse it, slide it back in and thus accomplish asuitable scale change along with appropriate adjustment of the rangeselector switch 118. Tolerance range slide 21a is also shown in FIG. 9to clip around the bracket 214.

The second indicator unit 16' is adapted to be mechanically connectedadjacent and in parallel with the unit 16 and electrically interwiredtherewith to use the same power supply but to receive signals from asecond probe (not shown). The two probes may, of course, be associatedwith the same or different parts and provide a convenient comparison dueto the adjacent and aligned disposition of the two display units 16 and16'.

Following the concept of modular add-on units, it is also within thescope of the present invention to provide a unit, similar to displayunit 16', for performing mathematical functions such as addition andaveraging such that signals from several probes or from successivereadings on a single probe may be mathematically processed as desired.It is noteworthy that the provision of a digital sign signal isparticularly amenable to microprocessors of the type now well known inthe art such that the microprocessor may be prewired and prebuilt in thefactory and shipped to the end user for straightforward electricalinterconnection with existing display units.

To assist the practitioner in constructing the invention, the majorcircuit blocks of FIGS. 1, 2, 4 and 7 have been labeled with theidentifying numbers of commercially available integrated circuit packswhich perform the required functions. It will be appreciated, however,that many different implementations are possible.

It is to be understood that the subject invention has been described byreference to specific embodiments and that many additions andmodifications thereto will be apparent to those skilled in the art.Accordingly, the foregoing description is not to be construed in alimiting sense.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A sizing gage having acolumnar display for indicating the measured sense and degree of partsize deviation from a mean size comprising: probe means for measuringpart size; display means including a plurality of individually excitableindicators; means exciting one of said indicators in response tomeasuring a part of said mean size and also including means exciting theindicators on opposite sides thereof in response to measuring incrementsof part size deviation of respectively opposite sense; said meansincluding: first signal means for generating a first waveform therelative timing corresponding to a size reference; second signal meansconnected to said probe means for generating a second periodic waveform,said second signal including means varying the relative timing of saidsecond waveform in accordance with measured size of said part;comparator means sensing the degree and sense of the timing differenceof said first and second waveforms; third signal means responsive tosaid comparator means producing a digital count corresponding to saiddegree of relative timing difference between the first and secondwaveforms; fourth signal means responsive to said comparator meansproducing a signal corresponding to the sense of said relative timingdifference; and addressable control means connecting the third andfourth signal means to the display means and responsive to the characterof said count and sense to excite a particular one of said indicators.2. Apparatus as defined in claim 1 wherein said indicators are arrangedlinearly.
 3. Apparatus as defined in claim 2 wherein the one of saidindicators representing said mean size is located centrally of saidlinear array.
 4. Apparatus as defined in claim 1 wherein the indicatorsprovide a visual signal upon excitation thereof, said one of saidindicators being of a different visual character than the remainder ofsaid indicators.
 5. Apparatus as defined in claim 4 wherein saidindicators are light-emitting diodes.
 6. Apparatus as defined in claim 1including scale means disposed adjacent said indicators for indicatingthe absolute value and sense of the part size deviation.
 7. Apparatus asdefined in claim 6 including means movable over said scale means forindicating tolerance limits.
 8. Apparatus as defined in claim 1 whereinsaid probe means comprises first and second normally balanced sensingcircuits, part contacting means for altering the balance between saidcircuits according to part size, and output circuit means for producingan electrical signal indicating the degree and direction of imbalance.9. Apparatus as defined in claim 8 wherein the output means comprises atransformer circuit having a primary coil and a secondary coil, thesignal across said secondary coil being nominally zero for balancedcircuit conditions and of increasing amplitude of positive and negativepolarity for respectively opposite directions of electrical imbalance insaid probe means, the amplitude of the signal across said secondarybeing an indication of the degree of electrical imbalance.
 10. Apparatusas defined in claim 1 wherein the second signal means includes amplifiermeans connected to said probe means for producing an alternatingwaveform representing part size deviation.
 11. Apparatus as defined inclaim 10 including means for generating an alternating currentexcitation signal, means for applying the alternating current signal tothe probe for exciting same, and selectively variable means for mixing avariable portion of the ac signal with the output of the probe fornulling the output signal from the amplifier means.
 12. Apparatus asdefined in claim 11 including selectively variable means for controllingthe gain of said amplifier means.
 13. Apparatus as defined in claim 12wherein said selectively variable means is a range selector comprising aplurality of range-selecting electrical components, and dial means forindividually connecting said components to said amplifier means forvarying the gain thereof.
 14. Apparatus as defined in claim 12 whereinsaid selectively variable means comprises a high-gain resistor andpush-button means for temporarily connecting said resistor to theamplifier means for increasing amplifier gain during a nullingprocedure.
 15. Apparatus as defined in claim 10 including sample gatemeans connected to the output of the amplifier means, means forconnecting the ac signal to the sample gate to control the opening ofthe sample gate in fixed phase relationship with the probe excitationsignal.
 16. Apparatus as defined in claim 15 including dc voltagestorage means connected to the output of the sample gate for providing adc voltage of amplitude and polarity representing the average amplitudeand polarity of the sampled pulses applied thereto, said dc voltagebeing connected to said second means such that the relative timing ofsaid second periodic waveform varies according to the dc value of thestored signal.
 17. Apparatus as defined in claim 1 further includingoscillator means for producing a fixed frequency alternating waveform,means for applying a signal related to said waveform to said probe meansfor excitation thereof, and means for applying said waveform to saidfirst and second signal means as a time base for generation of saidfirst and second waveforms.
 18. Apparatus as defined in claim 17including output means associated with said probe means and responsiveto part size deviations to produce an output signal of amplitude andpolarity related to the degree and sense of part size deviation,respectively, and adjustable nulling means connecting selectivelyvariable portions of the alternating waveform to said probe output foradjusting the probe output to zero.
 19. Apparatus as defined in claim 18including a sample gate connected to receive the probe output for gatinga signal proportional to the probe output to said second signal means,said alternating waveform being connected to said sample gate as acontrol signal for controlling the sample times during which said probeoutput is sampled whereby all of the sampled probe output signals are ofthe same polarity for a part size deviation of given sense. 20.Apparatus as defined in claim 19 further including means for connectinga signal related to the alternating waveform to the first and secondsignal means as a common time reference.
 21. Apparatus as defined inclaim 1 wherein said first and second waveforms are substantiallyperiodic squarewaves of alternating amplitude level, said third signalmeans comprising EXCLUSIVE OR gate means connected to receive the firstand second periodic waveforms and to produce an output signal only whenthe waveforms are dissimilar, and gate means connected to receive a highfrequency clock signal and the output of said EXCLUSIVE OR gate meansthereby to pass said high frequency signal as a digital countproportional in number to the duration of the output of said EXCLUSIVEOR gate, that is phase locked to the reference frequency.
 22. Apparatusas defined in claim 1 further including a digital counter connected toreceive said digital count and having a plurality of output linesseparately energizable in response to respective counts, saidaddressable control means being responsive to a selected output line ofthe counter and said sense signal for selecting for excitation one ofsaid indicators.
 23. Apparatus as defined in claim 22 including a seconddecimal counter connected to receive overflows from the first counter torepresent the next higher order number of said count.
 24. Apparatus asdefined in claim 23 wherein said indicators are connected for excitationin a grid comprising row and column excitation conductors requiring acoincidence of two signals for selection of any given indicator. 25.Apparatus as defined in claim 24 wherein said column excitationconductors are divided into first and second groups representingopposite senses of part size deviation, said fourth signal meanscomprising a flip-flop connected to receive the first and secondperiodic waveforms and being set and reset to states representative ofthe relative timing therebetween, the output of said flip-flop beingconnected to gate means for directing the output of said second counterto respective first and second groups of column excitation conductorsaccording to the relative timing between said periodic waveforms. 26.Apparatus as defined in claim 1 further including an oscillator forproducing a repeating waveform, means for connecting the oscillator tothe first and second signal means, and a phase-locked loop connected tosaid oscillator to produce a digital pulse train of fixed relation tosaid repeating waveform, said phase-locked loop having the outputthereof connected to said third signal means for providing said digitalcount.
 27. In a sizing apparatus for use with probe means for measuringpart size and a columnar display for indicating the measured sense anddegree of part size deviation from a mean size comprising: display meansincluding a plurality of individually excitable indicators; said sizingapparatus including means exciting one of said indicators in response tomeasuring of mean size and further including means exciting theindicators on opposite sides thereof in response to sensing incrementsof part size deviation of respectively opposite sense; first signalmeans adapted to be connected to a probe means including means forgenerating a periodic wave form and means varying the relative timing ofsaid wave form in correspondence with the degree of measured part sizedeviation; and second signal means for producing a digital countcorresponding to the degree of variance in the timing of said periodicwaveform relative to a reference; third signal means for producing asignal corresponding to the sense of said relative timing; and,addressable control means connecting the second and third signal meansto the display means and responsive to the character of said count andsense to excite a particular one of said indicators.
 28. Apparatus asdefined in claim 27 wherein said indicators are arranged linearly and acentral one of said indicators represents said ideal size.
 29. Apparatusas defined in claim 28 wherein said one indicator provides a signal ofone character and the remainder of said indicators provide a signal ofanother distinct character.
 30. Apparatus as defined in claim 29 whereinsaid indicators provide a visual output signal.
 31. Apparatus as definedin claim 27 wherein the first signal means comprises amplifier means forproducing an ac output signal the amplitude of which represents partsize deviation degree and the polarity of which represents the sense ofsaid deviation.
 32. Apparatus as defined in claim 31 including means forvarying the gain of said amplifier means.
 33. Apparatus as defined inclaim 32 wherein said gain varying means comprises a plurality of gaincontrol elements, and means for selectively connecting individualelements of said plurality into operative circuit relationship with saidamplifier to vary the measured deviation range.
 34. In a sizingapparatus for determining part size deviations and indicating the degreeand sense of a measured part size deviation from a nominally meandimension: display means including a plurality of linearly arrangedindividually excitable indicators, including means exciting one of saidindicators in response to sensing a part of said mean size and alsoincluding means exciting one of the indicators on opposite sides thereofin response to sensing increments of part size deviation of respectivelyopposite sense; a plurality of row excitation conductors interconnectingsaid indicators and a plurality of column excitation line conductorsinterconnecting said indicators such that the coincident selection forexcitation of a row and column line conductor operates to select a givenone of said indicators; means for producing a digital count signalrepresenting the degree of part size deviation detectable by a probe,means for producing a second digital signal including means responsiveto the sense of part size deviation detectable by a probe and meansresponsive to said count and second digital signals for selectingrespective row and column excitation line conductors corresponding tosaid degree and sense signals so as to select for excitation a given oneof said indicators.
 35. Apparatus as defined in claim 34 wherein saidindicators are light emitting diodes.
 36. Apparatus as defined in claim34 further including scale means disposed adjacent said linearlyarranged plurality of indicator means such that the excited indicator isrelated to a marking on said scale means.
 37. Apparatus as defined inclaim 34 wherein the count signal representing the degree of part sizedeviation is a digital pulse count, the combination including a counterhaving a plurality of separately energizable outputs connected tocontrol the row output for the row excitation conductors, means forproducing a pair of complemental signals representing respective sensesignals, means connecting one of said sense signals to one group ofcolumn excitation conductors, and means for connecting the other of saidsense signals to control a second group of column excitation conductorssuch that coincidental excitation of one of said counter outputs and oneof said sense signals excites an indicator representing the number insaid count and the sense of said part size deviation.
 38. In a sizingapparatus for use with a probe for measuring part size: display meansincluding a plurality of individually excitable indicators arrangedlinearly for indicating the degree and sense of part size deviation froma means size measured by said sizing apparatus; said sizing apparatusincluding means exciting one of said indicators in response to measuringa part of said mean size and also including means exciting theindicators on opposite sides thereof in correspondence with measuredincrements of part size deviation of respectively opposite sense; probemeans including means for defining a pair of interconnected currentloops having a common leg, tuning means including means for altering thecurrent through said common leg in correspondence with measured partsize, output means for producing an output signal corresponding to thepolarity and amplitude of current through said common leg, and avariable gain amplifier means connected to receive said output meanssignal and to produce an amplifier signal corresponding to the polarityand amplitude of the output signal; and means connected to said displaymeans exciting a given one of said indicators in correspondence with thepolarity and amplitude of said amplifier output signal.
 39. Apparatus asdefined in claim 38 including alternating voltage means connected toexcite said current loops and selectively variable nulling means forconnecting a portion of said alternating signal to said output means fornulling the output signal independent of said tuning means. 40.Apparatus as defined in claim 39 further including selectively variablemeans connected to said variable gain amplifier for varying the gainthereof to represent various ranges of part size deviation increments byamplitude variations in the output of said variable gain amplifier. 41.A sizing apparatus for use with probe means for measuring part size andincluding: a columnar display including a plurality of individuallyexcitable indicators for displaying the degree of part size deviationmeasured from a mean size, first signal means adapted for connection toa probe for generating a periodic waveform and including means varyingthe relative timing of said waveform in correspondence with measuredpart size relative to said mean size, second signal means for producinga digital count representing the degree in variation of timing of saidperiodic waveform relative a reference, and control means for connectingthe digital count to the display and responsive to the numberrepresented by said count to excite a particular one of said indicators.42. Apparatus as defined in claim 41 wherein said control meanscomprises first and second counters for receiving the digital count andfor assuming respective states representing the digits of said count,coincident current excitation means for controlling the excitation ofsaid indicators in response to a coincident address consisting of firstand second signals, the output of one counter being connected as thefirst address signal and the output of the second counter beingconnected as the second address signal.
 43. Apparatus as defined inclaim 41 wherein said indicators are lights.
 44. Apparatus as defined inclaim 41 further including as part of said first signal means a variablegain amplifier, and means for selectively varying the gain of theamplifier for varying the range of part size deviation incrementsdetected and displayed by said apparatus.
 45. Apparatus as defined inclaim 41 including scale means removably disposed adjacent saidindicators.
 46. Apparatus as defined in claim 45 wherein the displaycomprises a housing, said scale means comprising a substantiallyvertically oriented bracket disposed on said housing and adapted toreceive said scale in sliding relationship therein.
 47. Apparatus asdefined in claim 46 wherein said scale comprises an elongated plasticstrip having a transparent portion through which said indicator meansmay be viewed and a printed portion adjacent said transparent portionand containing indicia representing part size deviation increments. 48.Apparatus as defined in claim 41 wherein said display means comprises ahousing having a base and a vertically upstanding portion, saidindicators being disposed linearly in said vertically upstandingportion.
 49. Apparatus as defined in claim 41 further comprising limitdetector means connected to receive said count and comprising means forselecting a limit, means responsive only to counts at least equal tosaid preselected limit and means for indicating the receipt of a countat least equal to said limit.
 50. A sizing gage for use with a columnardisplay for indicating the sense and degree of part size deviation froma mean size comprising: probe means for measuring part size; firstsignal means generating a first waveform the relative timingcorresponding to a size reference; second signal means connected to saidprobe means for generating a second periodic waveform and includingmeans varying the relative timing of said first and second waveform incorrespondence with measured size; third signal means responsive to saidfirst and second waveforms producing a digital count corresponding tothe relative timing difference between the first and second waveforms;fourth signal means responsive to said first and second waveformsproducing a signal corresponding to the sense of said relative timingdifference; and addressable control means for connecting the third andfourth signal means to a display for exciting said display according tothe character of said digital count and sense.
 51. Apparatus as definedin claim 50 further including an oscillator for producing a triangularwaveform, means for connecting the oscillator to the first and secondsignal means, and a phase-locked loop connected to said oscillator forproducing a digital pulse train of fixed relation to said triangularwaveform, said phase-locked loop having the output thereof connected tosaid third signal means for providing said digital count as a gatedportion of said digital pulse train.
 52. A sizing gage having a columnardisplay for indicating the sense and degree of measured part sizedeviation from a mean size comprising: display means including aplurality of linearly arranged individually excitable indicators; saidsizing gage including means exciting one of said indicators in responseto measuring a part of said mean size and further including meansexciting the indicators on opposite sides thereof in response tomeasuring increments of part size deviation of respectively oppositesense; timed based reference signal means; probe means for measuringpart size and producing an AC signal, said probe means including meansvarying the amplitude of said AC signal in correspondence with saiddegree of deviation measured in a part size and further includes meansvarying said AC signal to lead or lag said reference signal according tothe the sense of the measured deviation from said mean part size; meansfor adjusting the amplitude of said AC signal produced by the probemeans to zero for any given part measured by said sizing gage wherebythe size of said measured part defines the mean size; and coding meansinterconnecting the probe means with the display means and includingmeans exciting the said one indicator when the amplitude of said ACsignal of the probe means is zero and also including means exciting oneof the other indicators when the output of the probe means is other thanzero, the coding means further including means responsive to theamplitude and phase of the probe AC signal coincidentally selecting saidother indicator for excitation.
 53. Apparatus as defined in claim 52further including means for indicating sensed part size outside upperand lower limits defining part size acceptability relative to said meanssize including means for determining whether the probe output signal iswithin said limits and producing an indication whenever the measuredpart size exceeds one of the upper and lower size limits.